Neurophysiological, neuroanatomical, ablation-behavioral and psychophysical studies are directed toward developing an understanding of the significance of topographic sensory representations; toward defining neural mechanisms that relate to and account for specific aspects of auditory and somatosensory sensation and behavior; and toward defining the nature and rules by which map dimensions of topographic representations in the somatosensory and auditory systems in primates are subject to modification as a function of use. In parallel studies, a model of stroke will be examined to determine by what rules input that loses its cortical target(s) can regain a cortical foothold via use-dependent competition with surrounding always-normal cortex. Studies in auditory cortex will employ diotic and free sound field stimulation, in studies in alert and anesthetized cats, squirrels and owl monkeys, along with electrical microstimulation and subfield microablation strategies. A principle objective will be to determine the functional significance of individual subfields of Al. Special emphasis will be placed on definition of the nature of higher-level representations of pitch and sound location, within appropriate subfields. Organizational principles will also be revealed in correlative anatomical-physiological studies, designed to demonstrate the brain stem sources on input to individual Al subfields, and to reveal the geometries of projections from level to level in this complexly organized system. These results will be related to somatosensory and auditory psychophysics and should provide basic information about how these sensory systems are organized to account for their perceptual and behavioral products.